In this grant, we describe novel transposon piggyBac vectors engineered to deliver transgenes as efficiently as currently available piggyBac systems, but with significantly less helper DNA co-delivered into the host genome. To generate these plasmids, we first identified an important and previously unreported aspect of transposon biology, that the full-length terminal domains required for successful plasmid-to-chromatin transgene delivery can be removed from the transgene delivery cassette without impairing transposition efficiency, as long as these terminal domains are present somewhere within the plasmid. Transposons have the capacity to carry a large cargo load and therefore represent an alternative to retroviral and lentiviral delivery of genes. While transposons do not generate an immune response like retroviruses, current transposons still deposit large amounts of helper DNA into the host genome, DNA that can produce long-term problems due to its retained enhancer and promoter activity. In this grant, we present our data on the construction and testing of these modified minimal transposon plasmids which represent a novel, and potentially safer, methods to deliver transgenes in vitro and in vivo. In this project we will move towards the commercialization of these vectors by determining their efficacy in delivering different sized fragments (Task 1) to multiple different cell types (Task 2). At the conclusion of this Phase I proposal, we will demonstrate that these re-designed transposons can deliver a wide range of DNA fragments to multiple different primary cell types.